The invention relates to the use of the soft output Viterbi algorithm (SOVA) in data transmission systems.
Many data transmission systems use a soft detector to generate for error correction code inputs both hard (1 or 0) decisions and corresponding confidence levels (referred to as “soft decisions”). The soft detector allows a decoder to achieve better decoding performance than would be possible if the decoder were to receive as input hard decisions only. Examples of soft detectors include maximum a-posteriori probability (MAP) detectors and soft output Viterbi algorithm (SOVA) detectors.
When a non-binary code over GF(2q) where q>1, for example, a Reed Solomon code, is used for error correction purposes, each q-bits in the codeword is treated as a symbol. Thus, for such a code, a soft detector must be capable of delivering symbol-level hard and soft decisions. The processing of the MAP detector, though capable of delivering symbol-level soft values, is extremely time-consuming and complex, as it considers 2q possible candidates for each symbol position. The known SOVA detectors, while less complex than the MAP detectors, operate only at the bit-level.